// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_BASE_DRAGDROP_DROP_TARGET_WIN_H_
#define UI_BASE_DRAGDROP_DROP_TARGET_WIN_H_

#include <objidl.h>

#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "ui/base/ui_base_export.h"

// Windows interface.
struct IDropTargetHelper;

namespace ui {

// A DropTarget implementation that takes care of the nitty gritty
// of dnd. While this class is concrete, subclasses will most likely
// want to override various OnXXX methods.
//
// Because DropTarget is ref counted you shouldn't delete it directly,
// rather wrap it in a scoped_refptr. Be sure and invoke RevokeDragDrop(m_hWnd)
// before the HWND is deleted too.
//
// This class is meant to be used in a STA and is not multithread-safe.
class UI_BASE_EXPORT DropTargetWin : public IDropTarget {
public:
    // Create a new DropTarget associating it with the given HWND.
    explicit DropTargetWin(HWND hwnd);
    virtual ~DropTargetWin();

    // IDropTarget implementation:
    HRESULT __stdcall DragEnter(IDataObject* data_object,
        DWORD key_state,
        POINTL cursor_position,
        DWORD* effect) override;
    HRESULT __stdcall DragOver(DWORD key_state,
        POINTL cursor_position,
        DWORD* effect) override;
    HRESULT __stdcall DragLeave() override;
    HRESULT __stdcall Drop(IDataObject* data_object,
        DWORD key_state,
        POINTL cursor_position,
        DWORD* effect) override;

    // IUnknown implementation:
    HRESULT __stdcall QueryInterface(const IID& iid, void** object) override;
    ULONG __stdcall AddRef() override;
    ULONG __stdcall Release() override;

protected:
    // Returns the hosting HWND.
    HWND GetHWND() { return hwnd_; }

    // Invoked when the cursor first moves over the hwnd during a dnd session.
    // This should return a bitmask of the supported drop operations:
    // DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
    // DROPEFFECT_MOVE.
    virtual DWORD OnDragEnter(IDataObject* data_object,
        DWORD key_state,
        POINT cursor_position,
        DWORD effect);

    // Invoked when the cursor moves over the window during a dnd session.
    // This should return a bitmask of the supported drop operations:
    // DROPEFFECT_NONE, DROPEFFECT_COPY, DROPEFFECT_LINK and/or
    // DROPEFFECT_MOVE.
    virtual DWORD OnDragOver(IDataObject* data_object,
        DWORD key_state,
        POINT cursor_position,
        DWORD effect);

    // Invoked when the cursor moves outside the bounds of the hwnd during a
    // dnd session.
    virtual void OnDragLeave(IDataObject* data_object);

    // Invoked when the drop ends on the window. This should return the operation
    // that was taken.
    virtual DWORD OnDrop(IDataObject* data_object,
        DWORD key_state,
        POINT cursor_position,
        DWORD effect);

private:
    // Returns the cached drop helper, creating one if necessary. The returned
    // object is not addrefed. May return NULL if the object couldn't be created.
    static IDropTargetHelper* DropHelper();

    // The data object currently being dragged over this drop target.
    scoped_refptr<IDataObject> current_data_object_;

    // A helper object that is used to provide drag image support while the mouse
    // is dragging over the content area.
    //
    // DO NOT ACCESS DIRECTLY! Use DropHelper() instead, which will lazily create
    // this if it doesn't exist yet. This object can take tens of milliseconds to
    // create, and we don't want to block any window opening for this, especially
    // since often, DnD will never be used. Instead, we force this penalty to the
    // first time it is actually used.
    static IDropTargetHelper* cached_drop_target_helper_;

    // The HWND of the source. This HWND is used to determine coordinates for
    // mouse events that are sent to the renderer notifying various drag states.
    HWND hwnd_;

    LONG ref_count_;

    DISALLOW_COPY_AND_ASSIGN(DropTargetWin);
};

} // namespace ui

#endif // UI_BASE_DRAGDROP_DROP_TARGET_WIN_H_
